The present invention relates to compound change gear vehicular transmissions of the type having an auxiliary section connected in series with a mechanical main transmission section. More particularly, the present invention relates to such a transmission of the type in which at least one of the sections, and preferably whichever section comprises the front section, is of the multi-countershaft type.
Furthermore, the present invention relates to vehicular transmissions of the type described above, in which it is desired to provide the transmission with some sort of power-take-off (PTO) capability, whereby engine horsepower which is transmitted through the transmission is available for driving some sort of auxiliary device. For example, a truck equipped with a transmission of the type to which the invention relates may also include a device such as a winch, a tailgate, a post hole digger, a dump body, etc., which may be operated by the vehicle driver while the truck is stationary and the engine is running.
Although the present invention may be utilized in various types of change gear transmissions, it is especially suited for use in a transmission including a front, mechanical main transmission section, and a rear, auxiliary section. By way of example only, the rear, auxiliary section could comprise a range box. Furthermore, the present invention is especially suited for use in such a transmission in which the front transmission section is of the twin countershaft type, and will be described in connection therewith. Twin (i.e., multiple, substantially identical) countershaft transmissions of the general type to which the present invention relates are well known in the art and are illustrated and described in detail in U.S. Pat. No. 3,105,395, assigned to the assignee of the present invention and incorporated herein by reference.
In a known, prior-art, PTO arrangement for use with a twin countershaft transmission, one of the countershafts is provided with a permanent, fixed shaft extension member which extends axially from the end of the front section countershaft through the rear section, and out through the rear wall of the transmission rear section. The PTO device is then mounted on the rear wall of the transmission rear section, with the input to the PTO device being the front section countershaft extension member.
Although such a prior art arrangement is generally acceptable, functionally, the arrangement has certain drawbacks. As is well known to those skilled in the art, it is not acceptable to have the PTO device in continuous engagement with its input (the countershaft extension member), and typically, PTO devices include some sort of arrangement for declutching the PTO relative to its input. The result of the prior art arrangement is that the total PTO package connected to the exterior of the rear wall of the transmission is quite large and cumbersome. As a further result, the PTO package increases the "installed length" of the overall transmission, such that in certain short wheel base vehicles, the particular transmission and PTO assembly cannot be used. Instead, it becomes necessary to use what is known in the art as a "side mount" PTO, thus increasing the overall lateral dimension of the transmission and PTO assembly.
Another disadvantage of the known, prior art arrangement is the necessity for a separate oil pump, typically driven off the PTO input shaft, to provide a flow of lubricant to the PTO gear set. The need for a lube pump, dedicated to the PTO device, adds further to the overall size, complexity, and expense of the PTO arrangement.